 (defn have-child?
   "Indicates whether x and y had a child together"
   [x y]
-  (fresh [z]
-    (male x)
-    (female y)
-    (parent x z)
-    (parent y z)
-    ))
+  (fresh [z] (father x z) (mother y z)))
 
 (defn get-couples []
   (run* [parents]

      (=== parents [x y]))
    ))

(defn tests []
  (pldb/with-db family-facts-db
    (println (get-ancestors 'Herb))
    (println (get-grand-parents 'Herb))
    (println (get-couples))
    ))


  (pldb/db
    [male 'John]
    [male 'Herb]
    [male 'Mike]
    [female 'Alice]
    [female 'Jessy]
    [female 'Nicola]
    [parent 'John 'Alice]
    [parent 'John 'Mike]
    [parent 'John 'Nicola]
    [parent 'Jessy 'Alice]
    [parent 'Jessy 'Mike]
    [parent 'Alice 'Herb]
    ))

(defne father [x y] ([x y] (parent x y) (male x)))
(defne mother [x y] ([x y] (parent x y) (female x)))

(defn is-grand-parent?
  "Indicates whether x is a grand-parent of y"
